This invention relates generally to an internal combustion engine operating on an emulsion of fuel and water and more specifically to cooling the fuel emulsion being returned from a fuel rail.
Engine manufacturers, governments, environmentalists, and consumers are all concerned with reducing pollution created from combusting a fuel and air mixture. Typical pollutants include an uncertain mixture of oxides of nitrogen (NOx), carbon monoxide (CO), unburned hydrocarbons (UHC), and particulates. Each of these pollutants generally forms through different combustion mechanisms or at different stages of combustion. Most of the pollutants decrease with increased engine efficiency. Increasing a flame temperature of combustion is one manner of increasing engine efficiency. In general, higher flame temperatures reduce UHC and CO types of pollution.
Conversely, NOx generally increases as the flame temperature increases. NOx currently may be reduced in the following manners: a) after treatment, b) reformulated fuels, c) exhaust gas recirculation, d) water injection, and e) operating engine at lower loads. Each of the above manners has associated problems. For example, after treatment currently requires additional hardware. Reformulated fuels may lead to a reduction in power, redesign of current engines, and additional hardware on the engine. Exhaust gas recirculation and water injection both attempt to reduce localized in-cylinder temperatures by the addition of a diluent. Exhaust gas recirculation reduces the engine efficiency. Water injection requires both additional hardware (including a water storage tank and a water injector) and a clean water supply. Another option may be to operate the engine at a less than optimal condition, but other forms of pollution may then increase.
A fuel emulsion operates similar to water injection without the need for a fresh supply of water or additional water injectors. The fuel emulsion suspends water in an oil-based fuel or suspends an oil-based fuel in water. In any event, the water reduces the flame temperature. Since the water and fuel are blended, one injector may deliver the fuel emulsion instead of using a separate water injector and fuel injector.
While the fuel emulsion operates generally like the oil-based fuel or water initially, fuel emulsions can break down into their components in high temperature and/or high shear stress conditions. In most fuel systems, the fuel starts at an ambient temperature and ambient pressure in a fuel tank. In many systems, a fuel line passes through or is formed in the engine block or an engine head. As the fuel passes through the fuel line, the fuel increases in temperature. These temperatures may range upwards of 100xc2x0 C. As more of the fuel emulsion is returned from the engine back to the tank, a bulk temperature of the fuel emulsion in the tank will increase in temperature. Some surfactants in the fuel emulsion may have reduced ability to hold the water and fuel together at the increased temperatures.
The increased temperature of the fuel emulsion may also lead to boiling off of a constituent having a low boiling point. A fuel transfer pump and/or intensifier will increase the pressure of the fuel emulsion in the fuel lines above the pressure of the fuel emulsion in the tank. While the fuel emulsion is at a high temperature and high pressure, a boiling point of the constituent may be sufficiently above the temperature of the fuel emulsion. However, the expansion of the fuel emulsion to the pressure of the tank may greatly lower the boiling point of the constituent and result in the constituent flashing into a gaseous phase. This becomes even more problematic where the engine is operating at a high altitude. At the high altitude, the pressure in the tank will be below pressures experienced at sea level. The gaseous phase in the return lines may cause erroneous readings of sensors in the return lines and/or venting of the constituent.
The present invention is directed at overcoming one or more of the problems set forth above.
In one aspect of the present invention a fuel emulsion injection system for an internal combustion engine has a fuel tank. A fuel rail fluidly connects with the fuel tank. Fuel injectors fluidly connect with the fuel rail. A fuel return line connects to a return side of the fuel rail and to the fuel tank. A fuel cooling device fluidly connects with the fuel return line. The fuel cooling device reduces a temperature of a fuel emulsion.
In another aspect of the invention, a method prevents dissolution of a fuel emulsion in a pressurized fuel system for a compression ignition engine by cooling the fuel emulsion returning from a fuel injector to a temperature below a prescribed temperature and expanding the fuel emulsion to the pressure of a fuel tank.